System and method of determining a mobile station&#39;s position using directable beams

ABSTRACT

A system and method for accurately determining the position of a mobile unit operating within a predefined service area is disclosed. Three embodiments of the present invention are disclosed which teach the use of one, two and three narrow beam base transceiver stations in the determination of a mobile unit&#39;s position. Where one base station is utilized, an information map of signal attributes is used in the position determination. Where two and three base stations are used, signal strength measurements in combination with the time difference of arrival of a signal at the various base stations are used in the position determination.

RELATED APPLICATIONS

The present application is a divisional of co-pending and commonlyassigned U.S. patent application Ser. No. 08/892,946, entitled SYSTEMAND METHOD FOR 911 CELLULAR LOCATION DETERMINATION, filed Jul. 15, 1997,the disclosure of which is incorporated herein by reference. Referenceis hereby made to the following four and commonly assigned U.S. patentapplications: NARROW BEAM WIRELESS SYSTEMS WITH ANGULARLY DIVERSEANTENNAS, Ser. No. 08/726,277, issued May 26, 1998 as U.S. Pat. No.5,757,318; METHOD AND APPARATUS FOR IMPROVED CONTROL OVER CELLULARSYSTEMS, Ser. No. 08/582,525, issued Mar. 16, 1999, as U.S. Pat. No.5,884,147; CELLULAR SYSTEM SIGNAL CONDITIONER WHICH OVERRIDES ADISCONNECT FOR ACTIVE RADIOS WIRELESSLY COMMUNICATING WITH MOBILESLOCATED IN PRE-IDENTIFIED TERRITORIAL POSITIONS, Ser. No. 08/651,980,issued Jul. 14, 1998, as U.S. Pat No. 5,781,864; and SYSTEM AND METHODFOR CELLULAR BEAM SPECTRUM MANAGEMENT, Ser. No. 08/651,981, issued Apr.28, 1998, as U.S. Pat. No. 5,745,841, the disclosures of whichapplications are incorporated herein by reference.

TECHNICAL FIELD

This invention relates to cellular communications, and morespecifically, to the determination of a mobile cellular communicationdevice location when operating within a cellular system.

BACKGROUND

Since its introduction for use by the general public in the early1980's, mobile communications, utilizing cellular telephone technologyhas experienced phenomenal growth. When initially introduced,infrastructure costs associated with establishing mobile switchingoffices (MSO) as well as the various base transceiver stations (BTS)providing signal coverage defining communication cells, caused cellulartelephony to be expensive to the user. Likewise, these infrastructurecosts demanded that cellular service providers (CSP) initially providecellular service only in metropolitan areas where the number ofpotential subscribers would be maximized.

As cellular service areas have matured, and the number of subscribershave grown, CSPs have continuously expanded their service areas toinclude less populated areas, and even rural service areas. Today it isnot uncommon, and even expected, that continuous cellular coverage willbe available to subscribers on extended cross country journeys.

This proliferation of cellular service has not only caused the serviceto be available to ever increasing areas of the country, but has alsodriven down the cost of the service such that it is affordable to alarge number of the population. It is common today not only for businesspersons to remain in touch with the office through the use of cellulartelephony but, due to their affordable nature, for family members toutilize the technology to remain in touch during leisure times as well.

This wide spread use of cellular communications has been a boon tosociety in that instant communication is very often available duringemergencies. It is not uncommon for passersby to possess a cellulartelephone and notify authorities, such as through dialing a local 9-1-1system, immediately upon the occurrence of a vehicular accident, evenwhen such an accident occurs in a remote area. Likewise, there have beennumerous occasions where a citizen has witnessed undesired behavior,such as operation of a vehicle under the influence of drugs or alcohol,and been able to notify authorities through the use of cellulartelephony before disastrous consequences have transpired.

However, as most enhanced 9-1-1 (E-9-1-1) systems are unable todetermine the position of a mobile phone, these reports to authoritiesare limited in their usefulness as they often are dependent on thecaller being able to accurately describe his/her position. Often times,a caller may not know his/her position with a great deal of certainty,or in the excitement of the moment may misstate the location.Furthermore, where the caller is the victim of the tragedy, the callermay be unable to clearly speak with the authorities so contacted, or mayhave only time enough to dial the 911 code.

Similarly, information regarding the position of a mobile unit may beuseful in the operation of the cellular system. For example, where knowngaps in cellular communication coverage exist in the system, suchposition information may be utilized by the system to adjust resourcesin order to avoid interruptions in the communication or to broadcast anannouncement that the service will continue when the gap is cleared.Utilization of such information to improve cellular communication isdisclosed in the above-referenced co-pending commonly assigned U.S.patent application entitled “Cellular System Signal Conditioner.”However, as the positioning information is utilized for system controloperations, as above, it is necessary to automatically determine themobile unit's position.

Therefore, it is advantageous for a cellular system to use a method toautomatically determine a mobile unit's position. Further fueling theimplementation of such capabilities are various government entitiesdirecting cellular operators to have the ability to determine thelocation of an active mobile communication unit within a predeterminedlevels of accuracy. Such demands dictate that an accurate and reliablesystem be developed and deployed rapidly. However, the above describedproliferation of cellular service necessitates that a great many BTSsites be adapted for such location determinations.

Current technology has utilized signal triangulation well known in theart to determine a mobile unit's location. However, such systems are bydesign limited to determining the position of origination of a signal incommunication with three spatially diverse BTSs.

In rural areas, where demand for cellular service is not great, BTSs aretypically spaced a maximum distance apart in order to provide cellularcoverage for as large an area as possible with as little infrastructurecost as is possible. These widely spaced BTSs provide a minimumcommunication overlap, and thus reduce the possibility of a mobilesystem being in communication with two such BTSs, much less the threeBTSs necessary for position triangulation. This problem is furtherexasperated by the fact that a great number of mobile units in use todayare of the handheld variety which utilize lower power thanvehicle-mounted units. These handheld units often experience marginalsignal strength even with the rural BTS nearest their position.Therefore, prior art systems for determining mobile unit position arevery limited in their usefulness in such areas.

In urban areas, where numerous BTSs are distributed in relatively closeproximity in order to provide increased capacity, it is often possibleto detect a mobile unit's signal on the three BTSs necessary fortriangulation. However, in urban environments, typically there existslarge structures causing reflected signals and, thus, erroneousmeasurements of distance as necessary for triangulation.

A need therefore exists in the art for a system and method enabling theautomated determination of position of a mobile communication unitoperating within the coverage area of a single radio transceiverstation.

A further need exists in the art for a system and method providing forthe accurate determination of the position of a mobile communicationunit, although operating within communication range of three radiotransceivers, who's signal is subject to indirect communication causedby ground clutter.

A yet further need exists in the art for a cost effective, yet accurateand reliable, system which may be implemented with a minimal amount ofinfrastructure cost associated with its deployment.

SUMMARY OF THE INVENTION

These and other objects, needs and desires are obtained in a system andmethod utilizing multiple narrow beams in conjunction with signalstrength and/or time difference of arrival information to determine thelocation of a mobile communication unit. Systems for implementingmultiple narrow beams in wireless communications are disclosed in theabove-referenced co-pending commonly assigned U.S. patent applicationentitled “Narrow Beam Wireless Systems With Angularly Diverse Antennas.”

Through the use of narrow beams at the BTS site, the present inventionis capable of accurately determining the position of a mobile unit whenable to detect its signal at as little as one BTS. However, in order tolocate a mobile unit who's signal is measurable at only a single BTSaccording to the present invention, an information map of the BTS'scoverage area must be developed.

Therefore, in a first preferred embodiment of the present invention aninformation map of a mobile unit's communication attributes at locationsthroughout the BTS's coverage area is developed. Such a map may consistof a signal strength map of the mobile unit's signal on each (or somesubset thereof) narrow beam when located at particular positions.Additionally, or in the alternative, such maps may consist of timedifference of arrival (TDA) of the signal coming in on one beam versusthe times on the other beams in communication with the unit when locatedat particular positions.

Likewise, as it is expected that a large number of mobile users will beautomobile born, road map information, or other representations ofcommon position possibilities, may be utilized. Utilizing road mapinformation in combination with direction information with respect tothe movement of the mobile unit, as may be determined throughreferencing changing signal conditions at ones of the multiple beams,the present invention may determine the mobile's position. Of course,where such road map information includes many possibilities as to amobile's position based on its direction, additional information, suchas signal strength to determine a distance from the BTS, may also beused. Furthermore, the information map may not only include the road mapinformation, but may also include the recorded signal attributesdescribed above.

Of course, all of the above described measurements may be made in theforward channel rather than the reverse channel, such as by transmittingdifferent signals on the various beams, if desired. Both forward andreverse channel measurements may be made to provide additionalconfidence in any location determination made. Of course, for forwardchannel measurements to be utilized in the location determination by theBTS, this information must be communicated from the mobile unit to theBTS. Therefore, the measurements in the reverse channel are preferred.

Through comparing the current attributes of a mobile unit's signal onthe various narrow beams of the BTS to the information map identifyingattributes with particular positions, a single BTS may accuratelypinpoint the position of the mobile unit. However, it shall beappreciated that such an embodiment of the present inventionnecessitates the pre-preparation of the information map so utilized.Although the information relationship so mapped for many positionswithin the BTS's coverage area may be interpolated or extrapolated fromactual field measurements, such information mapping still necessarilyrequires significant planning and setup in order to be operational.

Therefore, a second preferred embodiment of the present inventionutilizes two BTSs having narrow beams to determine the position of themobile unit. As above, this embodiment utilizes signal strength and TDAinformation in its determination of the mobile's location. However, astwo spatially diverse base units are utilized in the positiondetermination, the mapping of this information in advance of thedetermination is not necessary. Of course, measurements may be made inthe forward or reverse channels as discussed above, with respect toinformation mapping, if desired.

Through the use of two BTSs, the mobile unit's location may bedetermined by a first BTS determining the strongest narrow beams uponwhich the mobile's signal appears. The position of the mobile istypically within one such beam as the strongest signal indicates theshortest, most direct route, between the mobile and the base. However,as this information alone is insufficient to determine the position ofthe mobile more accurately than the coverage area of a narrow beam, asecond BTS is utilized.

The second BTS is able to use TDA information to independently determinetwo possible positions for the mobile. Thereafter, the locationdetermination may be made by comparing the information of the first andsecond BTSs. The single position of these two possible positionsdetermined by the second BTS which falls within the beams having thestrongest signal as determined by the first BTS will be the position ofthe mobile unit.

It shall be appreciated that this preferred embodiment of the presentinvention utilizes information shared between multiple BTSs. Moreover,in order to make the TDA determination, the second BTS preferably scansthe control channel of the first BTS. The number of narrow beams uponwhich the second BTS scans for the control channel of the first BTS maybe limited by referencing the information with respect to the beamshaving the strongest signal as determined at the first BTS. As such, itshall be understood that information communication between such BTSs isutilized by the present invention. Methods and apparatus forimplementing such intercommunication for actively managing callsthroughout a plurality of cells are disclosed in the above-referencedco-pending commonly assigned U.S. patent application entitled “Methodand Apparatus for Improved Control Over Cellular Systems.”

In a third preferred embodiment, a third BTS is utilized in the positiondetermination of the mobile. Of course, the combination of three basestations may be utilized to make the position determination through theaforementioned triangulation technique, if desired. Preferably, however,this third BTS is used to verify the position determination as made bytwo base stations described above. The third BTS is able toindependently confirm the mobile's position as determined through theuse of two base stations. Such independent confirmation is able toreveal anomalous position determinations and, thus, provide a higherlevel of confidence in the mobile's location.

It shall be appreciated from the foregoing, that a technical advantageof the present invention is realized by its ability to accuratelydetermine the position of a mobile communication unit by reference tosignals received at a single base station.

A further technical advantage of the present invention is that theposition of a mobile communication unit may be determined throughreference to a signal seen at only two base stations.

A yet further technical advantage of the present invention is that,through the optional use of the three base stations necessary for aposition determination in the prior art, a position determination may beindependently verified to a high degree of confidence.

Additionally, a technical advantage of the present invention is realizedin the fact that the method for determining position requires fewmodifications to systems in common use today and, therefore, is a costeffective and easy to implement solution to the mobile unit locationproblem.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand the specific embodiment disclosed may be readily utilized as a basisfor modifying or designing other structures for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe spirit and scope of the invention as set forth in the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWING

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a typical cellular communication system, utilizingmultiple beams;

FIG. 2 illustrates a positional arc, representing an outboard distancefrom a base station, to which the position of a particular mobile may benarrowed based on communication beam and distance information;

FIG. 3 illustrates time differential of arrival information arcsutilized to determine the position of a particular mobile; and

FIG. 4 illustrates the interconnection of the base transceiver stationsof a typical cellular communication system and an E-9-1-1-1 center.

DETAILED DESCRIPTION

Directing attention to FIG. 1, a typical arrangement of multibeamcellular base stations may be seen as BTSs 110, 120, and 130. It shallbe appreciated that each of the illustrated BTSs provides communicationcoverage throughout a predefined area through the use of twelve narrowbeams, shown as beams 1 through 12 associated with each BTS. Each ofthese beams provides substantially 30° azimuthal coverage and arearranged such that their composite radiation pattern provides 360°coverage about the associated BTS. Each of the BTS's composite radiationpatterns are arranged to provide cellular coverage as is in common usetoday with respect to cellular telephony.

The azimuthal arrangement of the co-located beams of the BTSs provides adifferent “view” for each of the beam sources. This different viewresults in each beam source having angular diversity such that each beamsource receives a different signal wave front. The importance of thisangular diversity to various embodiments of the present invention willbe made more evident in the discussion below.

It shall be appreciated that, although the disclosed embodiments of thepresent invention utilize twelve beam systems, systems providingdifferent numbers of beams, and even a single beam, may be used.However, it shall be appreciated that the more narrow the beams used,the more likely a mobile unit's signal will be detectable on a pluralityof the beams, as is necessary in utilizing the present invention.

It will be understood that the method of determining a mobile unit'sposition of the present invention may be utilized in any number ofwireless communication systems, such as those providing personalcommunications services (PCS), and is not limited to the cellulartelephony system discussed herein.

Referring again to FIG. 1, mobile unit 140 is illustrated operatingwithin beam 9 of BTS 110. It is this mobile unit for which a positiondetermination is to be made in the example determinations discussedherein.

In a first preferred embodiment of the present invention, thedetermination of the position of mobile unit 140 may be made frominformation available at only BTS 110. It shall be appreciated that thedetermination of position with reference to a single base station isadvantageous where the particular mobile unit, for which positioninformation is desired, is located such that only a single BTS is incommunication therewith. For example, many rural areas are sparselypopulated with base stations as the economics associated with theirdeployment demand their placement so as to service a maximum area. Suchwide spacing of base stations results in many locations throughout theirservice area where a mobile unit's signal may be detectable at only asingle BTS.

Likewise, as a position determination utilizing information from aplurality of BTSs necessarily requires intercommunication of thisinformation, it may be advantageous to utilize a single BTS in aposition determination. For example, where intercommunication of BTSs isslowed due to heavy utilization, reference to a single BTS may bepreferred for the position determination, at least for an initiallocation fix. This initial fix can be refined as time goes on to yieldincreasingly more accurate location data.

In order to make a position determination with reference to only one BTSaccording to the present invention, an information map of the BTSsservice area must have first been made. Such an information map may bemade by recording various communication attributes of a signal receivedat the BTS while a test system is operated within the service area.

As the test system is operated, the recorded communication attributesare associated with the position from which the test system transmittedthe signal for which the attributes were recorded. The position of thetest system may be determined, for example, by an operator's referenceto known landmarks. Similarly, the creation of the information map mayinclude the use of positioning technology at the test system such as aglobal positioning system (GPS). This way the test system couldaccurately determine its position by reference to geosynchronoussatellites at each position for which test signal attributes arerecorded. It shall be appreciated that such systems may be fullyintegrated into the test system such that when a test signal istransmitted, so to is the position from which the signal wastransmitted. Thereafter, the BTS mapping the information could identifythe signal attributes recorded for various of the beams with theposition information provided by the GPS.

The communication attributes recorded by the BTS preferably consist ofeither signal strength information, or TDA information of the signal asreceived on the various beams of the BTS for different locations withinthe service area of the BTS. It shall be appreciated that the recordingof this information requires very little modification to base stationsin use today. For example, relative signal strength indications (RSSI)are generally already in use at a BTS in order to make hand-offdecisions. Systems utilizing such measurements for communicationmanagement are disclosed in the above-referenced co-pending commonlyassigned U.S. patent application entitled “System and Method forCellular Beam Spectrum Management.”

The calculation of arrival time difference of a signal simply requirescomparing the time the test signal was received at various beams of theBTS. Therefore, the recording of this information requires little morethan the addition of control algorithms and the utilization of datastorage capacity accessible by the BTS.

Determination of the mobile's position by a single BTS according to thepresent invention requires the use of a multibeam system, because it isthe difference between communication attributes of the signal at variousones of the multiple beams which provides the system with the ability todetermine a precise location. For example, mobile unit 140 illustratedin FIG. 1 may transmit a signal which is received on beams 8, 9, and 10of BTS 110. If the signal strength of a single beam, such as beam 9,were used to make the position determination, an arc segment throughthis beam representing the distance from the BTS consistent with thelevel of signal attenuation is as accurate of location determination ascan be made. Moreover, the accuracy of this arc may be effected byobstructions in the signal path between the mobile unit an the BTS.

A positional arc assuming no, or insubstantial, signal obstruction, isshown in FIG. 2 as arc 200. It can be seen that mobile unit 140 could belocated anywhere along arc 200, such as at position 210, and stillresult in the signal strength measured by BTS 110.

However, where the signal strengths of each of beams 8, 9, and 10 areused, an accurate position may be determined. This is so because,although there may be multiple positions in the one beam from which thesignal may result in the same signal strength on that beam, thecombination of signal strengths of the additional beams pinpoints thelocation. For example, in FIG. 2 mobile unit 140 is illustrated withinbeam 9 positioned nearer to beam 10 than to beam 8. This relativeposition can be expected to result in a stronger signal at beam 10 thanat beam 8.

Therefore, although the position of the mobile unit associated with aparticular signal strength within beam 9 may be anywhere along arc 200as discussed above, the signal strength detected on beams 8 and 10 willvary depending on the unit's azimuthal position. For example, if mobileunit 140 were located at position 210, the signal strength of beam 8would be expected to be stronger than that of beam 10. As such, a map ofsignal strengths of various beams associated with positions throughoutthe BTS service area may be utilized to accurately determine the mobileunit's position.

Similarly, TDA information of the signal received on various of thebeams may be utilized to determine the mobile's position. Here, however,the time difference of the signal as received on the various beams isrecorded. For example, referring again to FIG. 2, the time difference ofthe signal of mobile unit 140 between the signal received by beam 9 and10 will be less than the time difference between the signal received bybeam 9 and 8. This is so because the mobile unit is located nearer beam10 than beam 8. However, if the mobile unit were to move, for example,to position 210 the time difference between the signal received by beam9 and 10 will be greater than the time difference between the signalreceived by beam 9 and 8. As in the signal strength embodiment discussedabove, recording exemplary sets of this TDA information and theassociated position information, can be used to enable latterdeterminations of position through referencing TDA information. Ofcourse, TDA information can also be calculated, not measured, and usedrelatively in order to determine position.

Of course, both signal strength and TDA information may be recorded inthe information map, if desired. For example, the mobile's position maybe independently verified by referencing such dual information sets.

Similarly, a combination of information recorded in the information mapand information measurable or determinable real-time may be usedaccording to the present invention. For example, measured TDAinformation may be used in combination with a recorded signal strengthmap in the location determination.

It shall be appreciated that using a location map as described above isnot feasible in a typical omni or three sector system since there can bemultiple locations within the coverage of a sector having the samesignal strength or TDA values where the signal is not detectable withinanother sector of the system. However, by using a multibeam antennasystem, one can consistently record the signal strength on more thanjust a single beam. Therefore, if the mobile has the same signalstrength on a particular beam at various locations within the coverageof that beam, the probability of having the same signal strength readingat multiple locations on multiple beams is very low.

It shall be understood that, although an information map containing agreat many positions and their associated communication attributes maybe recorded through the use of the above described test system, many ofthe mobile unit's positions may be interpolated or extrapolated byreference to empirically measured data sets. Such position informationinterpolation may be utilized to determine positions to within varyingdegrees of accuracy depending on the amount of empirical data available.As such, a tradeoff exists between the number of test positions sampled,and therefore the amount of actual information storage space utilized,and the accuracy of the position determination. However, as regulationsrequire a degree of accuracy to within 300 (or some other finite number)feet, clearly some interpolation of position information may beutilized. Regardless of the resolution of the position determinationchosen, this preferred embodiment of the present invention requires thepreparation of a information map having recorded therein exemplarypositioning information.

To avoid the use of such mapping techniques, a second preferredembodiment of the present invention utilizes two BTSs, at least one ofwhich having narrow beams, to determine the position of the mobile unit.As above, this embodiment may utilize signal strength and TDAinformation in its determination of the mobile's location. However, astwo spatially diverse base units are utilized in the positiondetermination, the mapping of this information in advance of thedetermination is not necessary.

Directing attention once again to FIG. 1, it can be seen that, althoughmobile unit 140 is located within the service area of BTS 110, both BTS120 and BTS 130 have beams directed toward the mobile unit.Specifically, beam 2 of BTS 120 and beam 5 of BTS 130 are disposed to“see” mobile unit 140.

It shall be appreciated that, although the communication beams of BTSs120 and 130 are intended to provide communication coverage within theservice area demarcated by the cellular pattern, these beams typicallywill be able to detect the signals of mobiles operating beyond thecell's boundary. However, to avoid interference caused by mobile unitsoperating within the service area of other BTSs, different communicationchannels are typically assigned for use on neighboring BTSs and/or theirbeams able to communicate with a single mobile unit. Therefore, BTSsutilized to make position determinations according to the presentinvention are preferably adapted to monitor not only its own controlchannel, but also the control channels of neighboring BTSs. It shall beappreciated that monitoring of the neighboring BTS's control channelprovides a convenient means by which a BTS may detect the presence of amobile unit although not operating within the base station's own servicearea. Of course, a voice channel or other characteristic signal may alsobe used according to the present invention.

Through the use of two BTSs, the mobile unit's location may bedetermined by a first BTS determining the strongest narrow beams uponwhich the mobile's signal appears. The position of the mobile istypically within one such beam as the strongest signal indicates theshortest, most direct route, between the mobile and the base. Of course,other methods of determining the beams the mobile is most likelyoperating within may be used, if desired.

Directing attention again to FIG. 1, mobile unit 140 is located withinbeam 9 of BTS 110, near the boundary with beam 10 of BTS 110.Presumably, these two beams will provide the strongest signal to BTS110. For example, beam 9 will provide the strongest signal, provided nostructures obscure the signal path, as this is the shortest most directroute. Likewise, beam 10 will provide the second strongest signal as itprovides the second shortest signal route.

However, the signal strength information alone is insufficient todetermine the position of the mobile. Such information merely providesinformation regarding the distance between the mobile unit and the BTS,such as the positional arc discussed above.

To precisely determine the location of the mobile unit according to thispreferred embodiment, the second BTS uses TDA information toindependently determine two possible positions for the mobile. Referringto FIG. 3, the use of this TDA information to determine the position ofmobile unit 140 is shown. It shall be appreciated that, by monitoringthe control channel, voice channel, or the like of BTS 110, BTS 120 maydetect signals transmitted by mobile unit 140. For example, as beam 2 ofBTS 130 is disposed to view mobile unit 140, this beam is likely todetect its transmissions. As previously discussed, BTS 110 hasdetermined beams 9 and 10 to be receiving the strongest signal frommobile unit 140.

Receiving the mobile unit's signal on beams 9 and 10 of BTS 110 and beam2 of BTS 120 provides the system with three signal reception timesnecessary to make two TDA calculations. Of course, to make these TDAcalculations involving signals detected at two different BTSs,communication between the BTSs is necessary. Such communication may beprovided by a network control system already in place to provide systemcontrol for such items as hand offs, resource assignments, etcetera.Moreover, the position determinations of the present invention may bemade by such a network control system rather than by logic disposed atthe various BTSs of the system. Systems adaptable to provide suchintercommunication between BTSs as well as the logic to make thedescribed position determinations are disclosed in the above-referencedco-pending commonly assigned U.S. patent application entitled “Methodand Apparatus for Improved Control Over Cellular Systems.”

Directing attention to FIG. 4, interconnection of the various BTSsillustrated in FIG. 1 is shown. It shall be appreciated that, althoughBTS 110 and BTS 130 are shown interconnected through BTS 120, any meansof interconnection, either direct or indirect, may be used. For example,the BTSs may all be indirectly connected through a base controllerstation (BCS) or a mobile switching office (MSO), where desired.

Referring again to FIG. 3, the TDA information between the signalreceived by beam 9 of BTS 110 and beam 2 of BTS 120 is represented asarc 310 and the TDA information between the signal received by beam 10of BTS 110 and beam 2 of BTS 120 is represented as arc 300. It shall beappreciated that, due to the above described angular diversity, thesignal transmitted by mobile unit 140 will be received at beam 9 beforebeing received at beam 10, provided of course there are no obstructionsin beam 9. When this information is compared to the arrival time of thesignal at beam 2 of BTS 120, there will be a greater time difference ofarrival between beams 2 and 9 than between beams 2 and 10.

The possible positions of mobile unit 140 having the two determined timedifferences of arrival may be partially represented by arcs, such as arc300 and 310, having different curvature representing a greater or lesserdifference. It shall be appreciated that by having only one TDAcalculation, the same uncertainty of position is presented as with thesignal strength information alone as discussed above. However, utilizingtwo such TDA calculations, the crossover points of the associated arcsnarrows the possible positions to two.

Thereafter, the precise location determination may be made by comparingthe single position of these two possible positions which falls withinthe beams having the strongest signal. Here, the position of mobile unit140 will be the crossover point of arcs 300 and 310 which is locatedwithin beam 9 of BTS 110.

It shall be appreciated that the position determination of thispreferred embodiment of the present invention utilizes multiple beams atonly one of the two base stations. As such, it is possible to make aprecise determination of position in a cellular network even where notfully populated with multibeam BTSs.

Where additional base stations are capable of detecting a mobile unit'ssignal, such additional BTSs may be utilized in the positiondetermination to provide position verification or an additional degreeof confidence to the determination. Therefore, a third preferredembodiment utilizes a third BTS in the position determination of themobile. It shall be appreciated that the combination of three basestations, like the aforementioned triangulation technique, does notrequire the use of multiple beams at any of the base stations theposition determination.

Preferably, this third BTS is used to verify the position determinationas made by two base stations described above. Through the use of TDAcalculations based on the mobile unit's signal received on a beam of thethird BTS and those of the first BTS, the third BTS is able toindependently confirm the mobile's position as determined through theuse of two base stations. Such independent confirmation is able toreveal anomalous position determinations and, thus, provide a higherlevel of confidence in the mobile's location.

For example, referring again to FIG. 1, BTS 130 may be able to detectthe signal of mobile unit 140 on beam 5 much like described for BTS 120and beam 2. Thereafter, TDA calculations may be made for the signalreceived by beam 9 of BTS 110 and beam 5 of BTS 130 and the signalreceived by beam 10 of BTS 110 and beam 5 of BTS 130. This will providea point located within beam 9 of BTS 110 from which the position ofmobile unit 140 may be independently verified.

It shall be appreciated from the above discussion that utilizing threebase stations, as is required by current triangulation methods, allowsthe present invention to provide an additional degree of confidence inthe position determinations made. Of course, the use of this third BTSis not necessary for the position determination and may be omitted, ifdesired.

Similarly, an information map may be utilized in conjunction with, or inthe alternative to, the multi-BTS methods described above. For example,the information map may be utilized to confirm the locationdetermination made by the two BTS method. Likewise, the memory map maybe utilized in the event that heavy communication network trafficimpedes or slows communication between the two BTSs monitoring themobile unit's communication attributes.

Likewise, these different methods may be utilized to provide moreaccurate determinations of a mobile unit's position. For example, amethod providing less accuracy, but providing a hasty determination, mayinitially be used. Thereafter, a method providing greater accuracy, buta delayed determination, may be used to pinpoint the mobile unit'sposition.

Moreover, multiple determinations as to a mobile unit's location may bemade by the present invention. For example, the method used to make aninitial location determination may be repeated at a certain timeinterval to confirm the initial determination. Similarly, where atemporary anomaly provides an initially inaccurate locationdetermination, later determinations will reflect a more accuratedetermination when the anomaly has dissipated.

Regardless of the method used to determine the mobile unit's position,the present invention may communicate this determination to any numberof systems utilizing such information. For example, the locationinformation may be communicated to a BCS or MSO, or any other systemcontrolling functions of the communication network, for use in networkcontrol decisions. Moreover, the location itself can be sent to theother system, or the information used to determine the location may besent in its stead. Accordingly, the location may be determined at thecell site or at the controlling center.

Preferably, the location information is communicated to an E-9-1-1center for use in locating the source of an emergency call. Thisinformation may be communicated upon a determination of position and maybe updated thereafter upon refinement or updating of the locationdetermination. The communication of location information to the E-9-1-1center may be through a public switched network (PSN) as illustrated inFIG. 4, or may be by other means, such as direct lines coupling thecommunication network with the E-9-1-1 center.

Of course, the location information provided by the present inventionmay be utilized for services other than the aforementioned E-9-1-1service. For example, location information may be useful in providingspecialized service options. Such options might include billing based oncaller location, availability of optional or enhanced services based oncaller location, or the like.

Additionally, the communication between the communication network andthe service may be bi-directional. For example, once locationinformation is communicated to the E-9-1-1 center, the E-9-1-1 centermay respond with instructions for the communication system to lock thechannel used by the mobile unit for updated or refined locationdeterminations. Likewise, the instructions provided to the communicationnetwork by the E-9-1-1 center may include a request for additionallocation resources be used in subsequent location determinations. Forexample, the request may be for verification of the locationdetermination by one of the above discussed methods not used in theoriginal location determination. Of course, the present invention mayinstigate these instructions on its own accord in addition to, or in thealternative, to the E-9-1-1 system daily so, if desired.

It shall be appreciated that the above discussion has assumedsubstantially direct communication between the mobile unit and thevarious BTSs in order to simplify the description of the inventiveconcepts involved. However, it shall be appreciated that the methods ofthe present invention will provide an accurate determination of a mobileunit's position even when multipath signal reflections or other signalanomalies cause by structures are introduced. For example, theinformation map of the first preferred embodiment will simply recordexemplary information which includes the effects of these signalanomalies.

Similarly, utilization of two BTSs to determine the mobile's positionwill use the strongest signals (presumably a direct or nearly directsignal path) to determine the mobile's position from two possibilitiesdetermined from TDA information. The use of these two positiondetermining techniques, both signal strength and TDA information, tendsto ameliorate the effects of these signal anomalies. Of course, aspreviously discussed, the effects of these signal anomalies may befurther ameliorated through the use of redundant position determinationssuch as the use of information maps or signal detection at additionalBTSs, if desired.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims.

What is claimed is:
 1. A system for determining the position of awireless communication unit operating in a wireless communication systemhaving a plurality of communication arrays wherein at least a firstcommunication array includes a plurality of radiation beams disposed toprovide angular diversity, said system comprising: means for identifyingat said first communication array of said plurality of communicationarrays a first and second radiation beam of said plurality of radiationbeams detecting a signal associated with said wireless communicationunit; means for ascertaining a first time differential between saidsignal detectable at said first beam at said first communication arrayand said signal as detectable at a second communication array, saidmeans also for ascertaining a second time differential between saidsignal detectable at said second beam at said first communication arrayand said signal as detectable at said second communication array; andmeans operable with said identifying means and said ascertaining meansfor determining a position of said wireless communication unit.
 2. Thesystem of claim 1, further comprising: means for redetermining theposition of said wireless communication unit.
 3. The system of claim 2,wherein said position redetermination is made to confirm a previousposition determination.
 4. The system of claim 2, wherein said positionredetermination is made to update a previous position determination. 5.The system of claim 2, wherein said position redetermination is made torefine a previous position determination.
 6. The system of claim 1,wherein ones of said plurality of radiation beams are narrow beamshaving a beam width of less than 120°.
 7. The system of claim 1, whereinsaid wireless communication system comprises a cellular telephonecommunication system.
 8. The system of claim 1, wherein said wirelesscommunication system comprises a personal communication services system.9. The system of claim 1, wherein said determining means is operablewith an 9-1-1 system to provide caller location data substantiallycontemporaneously with an emergency call from said wirelesscommunication unit.
 10. The system of claim 9, wherein said data isprovided to said 9-1-1 system utilizing a link from the group consistingof a public switched network, a private communication line, and aprivate wireless link.
 11. The system of claim 1, wherein saiddetermining means is operable with a communication controller of saidwireless communication system.
 12. The system of claim 1, furthercomprising: means for recording a plurality of sample communication datasets including at least one communication attribute as detectable onones of said radiation beams associated with said first communicationarray; means for associating ones of said plurality of sample data setswith particular location within a predefined service area associatedwith said first communication array; and means for comparing attributesof said signals detected on said first and second beams with said samplecommunication data sets.
 13. The system of claim 12, wherein said sampledata sets comprise receive signal strength information.
 14. The systemof claim 12, wherein said sample data sets comprise signal timedifferential of arrival information.
 15. The system of claim 12, whereinsaid comparing means is independently operable to ascertain a positionof said wireless communication unit.
 16. The system of claim 15, whereinsaid comparing means is operable to provide said independentlyascertained position to an 9-1-1 system to provide additional callerlocation data.
 17. The system of claim 15, wherein said determiningmeans is operable to confirm said position ascertained by said comparingmeans.
 18. The system of claim 12, wherein said comparing means isoperable to confirm said position determined by said determining means.19. The system of claim 12, wherein said comparing means is operable toupdate said position determined by said determining means.
 20. Thesystem of claim 12, wherein said comparing means is operable to refinesaid position determined by said determining means.
 21. The system ofclaim 12, wherein said independently operable comparing means isoperable to ascertain a position substantially real time and said meansfor determining a position is operable dependent upon communicationsavailable between said first communication array and said secondcommunication array.
 22. The system of claim 1, further comprising:means for ascertaining a third time differential between said signaldetectable at said first beam at said first communication array and saidsignal as detectable at a third communication array, said means also forascertaining a fourth time differential between said signal detectableat said second beam at said first communication array and said signal asdetectable at said third communication array.
 23. The system of claim22, wherein said ascertaining means is operable with said identifyingmeans to independently determine a position of said wirelesscommunication unit.
 24. The system of claim 23, wherein saidindependently ascertained position is provided to an 9-1-1 system toprovide additional caller location data.
 25. The system of claim 23,wherein said determining means is operable to confirm said independentlydetermined position.
 26. The system of claim 22, wherein saidindependently determined position is utilized to confirm said positiondetermined by said determining means.
 27. The system of claim 22,wherein said independently determined position is utilized to updatesaid position determination by said determining means.
 28. The system ofclaim 22, wherein said independently determined position is utilized torefine said position determination by said determining means.
 29. Thesystem of claim 1, further comprising: means for locking a communicationchannel associated with said wireless communication unit for subsequentuse in determination of a position of said wireless communication unit.30. The system of claim 1, further comprising: means for activatingselect other resources in said wireless communication system suitablefor use in determination of a position of said wireless communicationunit, said select other resources being in addition to the identifyingmeans, ascertaining means, and determining means.
 31. The system ofclaim 30, wherein said activating means is operable upon instructionfrom a 9-1-1 system.
 32. A method for determining the position of acommunication unit operating in a communication system having aplurality of communication base stations, said base stations havingassociated therewith a plurality of directional radiation beams, saidmethod comprising the steps of: identifying at a first base station ofsaid plurality of base stations a first beam of said plurality of beamshaving a first desired signal attribute associated with saidcommunication unit; identifying at said first base station a second beamof said plurality of beams having a second desired signal attributeassociated with said communication unit; ascertaining a first timedifferential of arrival between a signal detectable at said first beamat said first base station and said signal as detectable at a beam at asecond base station; ascertaining a second time differential of arrivalbetween a signal detectable at said second beam at said first basestation and said signal as detectable as a beam at said second basestation; and determining a physical position of said communication unitby identifying an intersection point of intersection points of arcsassociated with said first time differential of arrival and said secondtime differential of arrival located in one of said first and secondbeams.
 33. The method of claim 32, further comprising the step of:utilizing said determination made in said determination step with anE-9-1-1 system.
 34. The method of claim 32, further comprising the stepof: utilizing said determination made in said determination step atleast in part to control said communication system.
 35. The method ofclaim 32, further comprising the steps of: recording a plurality ofsample communication data including at least one communication attributeas detectable at ones of said beams associated with said first basestation; associating data of said plurality of sample data with aparticular physical location; and comparing attributes of said signalsdetected on said first and second beams with said sample communicationdata.
 36. The method of claim 35, wherein said sample data comprisereceive signal strength information.
 37. The method of claim 35, whereinsaid sample data sets comprise signal time differential information. 38.The method of claim 35, further comprising the step of: utilizing saidcomparison made in said comparison step to verify said determinedphysical position of said communication unit.
 39. The method of claim 35further comprising the step of: determining a physical position of saidcommunication unit including reference to said comparison step.
 40. Themethod of claim 32, further comprising the steps of: ascertaining athird time differential of arrival between a signal detectable at saidfirst beam at said first base station and said signal as detectable at abeam at a third base station; and ascertaining a fourth timedifferential of arrival between a signal detectable at said second beamat said first base station and said signal as detectable at said beam atsaid third base station.
 41. The method of claim 40, further comprisingthe step of: utilizing said third and fourth time differentials toindependently determine a physical position of said communication unit.42. The method of claim 40, further comprising the step of: utilizingsaid third and fourth time differentials to confirm said physicalposition determined at said determining step.
 43. A system fordetermining the location of a radio operating within a cellularcommunication network having a plurality of base transceiver stations,said base transceiver stations having a plurality of narrow radiationbeams disposed to provide angular diversity, wherein said locationdetermination is utilized by a substantially automated 9-1-1 service,said system comprising: means for identifying at a first basetransceiver station of said plurality of base transceiver stations afirst and second radiation beam of said plurality of radiation beamshaving respectively a first strongest and a second strongest receivesignal associated with said radio; means for ascertaining a first timedifferential of arrival between a signal received at said first beamidentified with said first strongest signal at said first basetransceiver station and said signal as received at a beam at a secondbase transceiver station, wherein said first and second base transceiverstations provide adjacent areas of communication coverage; means forascertaining a second time differential of arrival between a signalreceived at said second beam identified with said second strongestsignal at said first base transceiver station and said signal asreceived at said beam at said second base transceiver station; meansoperable with said identifying means and said ascertaining means fordetermining a position of said radio; and means for communicating saiddetermined position to said 9-1-1 service.
 44. The system of claim 43,wherein said identifying means is operable with relative signal strengthindications as provided by said base transceiver station.
 45. The systemof claim 43, further comprising: means for verifying said positiondetermined by said determining means.
 46. The system of claim 43,further comprising: means for refining said position determined by saiddetermining means.
 47. The system of claim 43, further comprising: meansfor updating said position communicated to said 9-1-1 service.